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UNIT 1
Computers – historical review

(History of computing hardware)

Based on Wikipedia, the free encyclopedia


Prior to the advent of machines that resemble today's CPUs, computers such as ENIAC (Electronic Numerical Integrator and Computer) had to be physically rewired in order to perform different tasks. These machines are often referred to as "fixed-program computers" because of their need to be physically reconfigured in order to run a different program. Since the term "CPU" is generally defined as a software (program) executing device, the earliest devices that could rightly be called CPUs came with the advent of the stored-program computer.

The idea of a stored-program computer was already present during the design of the ENIAC, but was not initially used in that computer because of speed considerations. On 30 June 1945, before the ENIAC was even completed, a mathematician John von Neumann published the paper entitled "First Draft of a Report on the EDVAC (Electronic Discrete Variable Automatic Computer)". It outlined the design of a stored-program computer that would eventually be completed in August 1949. The EDVAC was designed to perform a certain number of instructions (or operations) of various types. These instructions could be combined to create useful programs for the EDVAC to run. Significantly, the programs written for the EDVAC were stored in high-speed computer memory rather than specified by the physical wiring of the computer. This overcame a severe limitation of the ENIAC, which was the large amount of time and effort it took to reconfigure the computer to perform a new task. With von Neumann's design the program or software, that the EDVAC ran, could be changed simply by changing the contents of the computer's memory.

It should be noted that while von Neumann is most often credited with the design of the stored-program computer because of his design of the EDVAC, others before him such as Konrad Zuse had suggested similar ideas. Additionally, the so-called Harvard architecture of the Harvard Mark I, which was completed before the EDVAC, also utilized a stored-program design using a punched paper tape rather than electronic memory. The key difference between the von Neumann and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both. Most modern CPUs are primarily von Neumann in design, but elements of the Harvard architecture are commonly seen as well.

Being digital devices, all CPUs deal with discrete states and therefore require some kind of switching elements to differentiate between and change these states. During the height of electromechanical and electronic computers, electrical relays and vacuum tubes (thermionic valves) were commonly used as switching elements. Although these had distinct speed advantages over earlier, purely mechanical designs, they were unreliable for various reasons. For example, building direct current sequential logic circuits out of relays requires additional hardware to cope with the problem of contact bounce. While vacuum tubes do not suffer from contact bounce, they must heat up before becoming fully operational and eventually stop functioning altogether. Usually, when a tube failed, the CPU would have to be diagnosed to locate the failing component so it could be replaced. In fact, early electronic (vacuum tube based) computers were generally faster, but less reliable than electromechanical (relay based) computers. Tube computers like the EDVAC tended to average eight hours between failures, whereas relay computers like the Harvard Mark I failed very rarely. In the end, tube based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems. Most of these early synchronous CPUs ran at low clock rates compared to modern microelectronic designs. Clock signal frequencies ranging from 100 kHz to 4 MHz were very common at this time, limited largely by the speed of the switching devices they were built with.


Discrete transistors and IC CPUs. The design and complexity of CPUs improved as various technologies facilitated building smaller and more reliable electronic devices. The first such improvement came with the advent of the transistor. Transistorised CPUs during the 1950s and 1960s no longer had to be built out of bulky, unreliable, and fragile switching elements like electrical relays and vacuum tubes. With transistors more complex and reliable CPUs were built onto one or several printed circuit boards containing discrete (individual) components.


During this period, a method of manufacturing many transistors in a compact space gained popularity. The integrated circuit (IC) allowed a great deal of transistors to be manufactured on a single semiconductor-based die, or "chip". At first only very basic non-specialized digital circuits such as NOR gates were miniaturized into ICs. CPUs based upon these "building block" ICs are generally referred to as "small-scale integration" (SSI) devices. SSI ICs, such as the ones used in the Apollo guidance computer, usually contained transistor counts numbering in multiples of ten. To build an entire CPU out of SSI ICs required thousands of individual chips, but still consumed much less space and power than earlier discrete transistor designs. As microelectronic technology advanced, an increasing number of transistors were placed on ICs, thus decreasing the quantity of individual ICs needed for a complete CPU. MSI and LSI (medium- and large-scale integration) ICs increased transistor counts to hundreds, then thousands.

In 1964 IBM introduced its System/360 architecture, which was used in a series of computers that could run the same programs with different speed and performance. This was significant at a time when most electronic computers were incompatible with one another, even those made by the same manufacturer. To facilitate this improvement, IBM utilized the concept of a microprogram (often called "microcode"), which still sees widespread usage in modern CPUs. The System 360 architecture was so popular that it dominated the mainframe computer market for the next few decades and left a legacy that is still continued by similar modern computers like the IBM zSeries. In the same year (1964), the Digital Equipment Corporation (DEC) introduced another influential computer aimed at the scientific and research markets, the PDP-8. DEC would later introduce the extremely popular PDP-11 line that originally was built with SSI ICs, but was eventually implemented with LSI components once these became practical. In stark contrast with its SSI and MSI predecessors, the first LSI implementation of the PDP-11 contained a CPU comprised of only four LSI integrated circuits.



Transistor-based computers had several distinct advantages over their predecessors. Aside from facilitating increased reliability and lower power consumption, transistors also allowed CPUs to operate at much higher speeds because of the short switching time of a transistor in comparison to a tube or relay. Thanks to both the increased reliability as well as the dramatically increased speed of the switching elements (which were almost exclusively transistors by this time), CPU clock rates in the tens of MHz were obtained during this period. Additionally, while discrete transistors and IC CPUs were in heavy usage, new high-performance designs like SIMD (Single Instruction Multiple Data) vector processors began to appear. These early experimental designs later gave rise to the era of specialized supercomputers like those made by Cray Inc.

Vocabulary





clock rate, clock frequency, clock speed


kmitočet hodin, taktovací frekvence, sloužící k synchronizaci operací počítače, mimo jiné určuje jakou rychlostí se provádějí operace procesoru; je pro daný procesor stabilní a je řízena jednotkou, která tuto rychlost procesoru udává bez ohledu na druh činnosti; taktovací frekvence je jedno z nejdůležitějších měřítek výkonnosti procesoru, i když není měřítkem jediným

contact bounce

kmitání kontaktů (relé),odskok kontaktů (relé)

debouncing

eliminace vlivu kmitání kontaktů

debouncing circuit

obvod eliminující kmitání kontaktů

chip set

čipová sada

physical wiring

fyzické propojení (zde konkrétní propojení)

semiconductor-based die or chip

čip též integrovaný obvod

switching time

doba přepínání

thermionic valve

elektronka

to bounce

kmitat, odrazit se zpět

vacuum tube, cathode-ray tube (CRT)


obrazovka, základní část monitoru nebo televizního přijímače – typ vakuové elektronky, zakončené stínítkem, na němž se vytváří obraz



Abbreviations





AC (Alternating current)

Střídavý proud

DEC (Digital Equipment Corporation )

DEC, výrobce počítačů (pohlcen HP)

EDVAC (Electronic Discrete Variable Automatic Computer)

Architektura elektronického počítače navržená von Neumannem v roce 1945 (realizováno v 1949)

ENIAC (Electronic Numerical Integrator and Computer)

Elektronický číslicový integrátor a kalkulátor, tj. elektronkový číslicový počítač zkonstruovaný roku 1946 v USA

IC (integrated circuit)

Integrovaný obvod

LSI (large- scale integration)

Velký stupeň integrace

MSI (medium-scale integration)

Střední stupeň integrace

PCB (Printed Circuit Board)

Deska tištěných spojů

SIMD (Single Instruction Multiple Data)

Jedna instrukce, vícenásobná data, tj. jedna instrukce se provádí na více datech, vektorové zpracování, vektorový procesor

SSI (small-scale integration)

Nízký stupeň integrace


Exercise 1 Make sentences putting the given words into a correct order:


  1. "First Draft of a Report on the EDVAC" - published - entitled - On 30 June 1945 - a mathematician - the paper - John von Neuman.

  2. EDVAC - could be combined - The instructions - to create - useful programs – for - the.

  3. CPUs - discrete states - these states – therefore – between - some kind – require - of switching – elements - to differentiate - and change – and - deal with - All.

  4. CPU - a vacuum tube - the failing component – When – the – failed - would have - to be diagnosed - to locate.

  5. Early – computers – but - electronic computers - generally faster – than - less reliable - were electromechanical.

  6. CPUs - the reliability – became – outweighed – problems - the significant - speed advantages – generally – dominant – because - Tube based.

  7. CPUs – electronic - and complexity - building smaller – facilitated – of – increased - as – technologies - and more reliable – various - The design - devices.



Exercise 2 Make questions concerning the words in bold italics:


  1. SIMD designs rely on the general-purpose portions of the CPU to handle the program details.

  2. SIMD instructions handle the data manipulation only.

  3. Smaller-scale SIMD operations have now become widespread in personal computer hardware.

  4. Today the term SIMD is associated almost entirely with these smaller units.

  5. First electronic computers needed to be physically rewired in order to perform different tasks.

  6. John von Neuman published the paper entitled "First Draft of a Report on the EDVAC" on 30 June 1945.

  7. Instructions of various types could be combined to create useful programs for the EDVAC to run.



Exercise 3 Fill in the gaps using words from the box below:


SSI transistors individual chip basic advanced increased counts space manufacturing

During the 1950s and 1960s, a method of … (1) … many transistors in a compact space gained popularity. The integrated circuits allowed a great deal of … (2) … to be manufactured on a single semiconductor-based die, or " … (3) … ". At first only very … (4) … non-specialized digital circuits such as NOR gates were miniaturized into ICs. CPUs based upon these "building block" ICs are generally referred to as "small-scale integration" ( … (5) …) devices. SSI ICs usually contained transistor … (6) … numbering in multiples of ten. Building an entire CPU out of SSI ICs required thousands of individual chips, which still consumed much less … (7) … and power than earlier discrete transistor designs. As microelectronic technology … (8) … , an increasing number of transistors were placed on ICs, thus decreasing the quantity of … (9) … ICs needed for a complete CPU. MSI and LSI ICs … (10) … transistor counts to hundreds, then thousands.



Exercise 4 Decide which answer (A, B, C, D) best fits each gap:

Contact bounce (also called chatter) is a … (1) … problem with mechanical switches and relays. Switch and relay contacts are … (2) … made of springy metals that are forced into contact by an actuator. When the contacts … (3) … together, their momentum and elasticity act together to cause bounce. The result is a rapidly pulsed electrical current instead of a … (4) … transition from zero to full current. The waveform is then further … (5) … by the parasitic inductance and capacities in the switch and wiring, resulting in a series of damped sinusoidal … (6) …. This effect is usually unnoticeable in AC main circuits, where the bounce happens too quickly to … (7) … most equipment, but causes problems in some analogue and logic circuits that are not designed to … (8) … with … (9) … voltages.




1

A

common

B

general

C

joint

D

ordinary

2

A

ordinarily

B

usually

C

generally

D

habitually

3

A

hit

B

knock

C

pound

D

strike

4

A

pure

B

clean

C

unadulterated

D

chaste

5

A

altered

B

shaped

C

modified

D

changed

6

A

vacillations

B

oscillations

C

fluctuations

D

variations

7

A

affect

B

influence

C

direct

D

induce

8

A

get by

B

cope

C

grapple

D

manage

9

A

swinging

B

varying

C

oscillating

D

vibrating








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