Editing GE 645 (section)

==System configuration==
The basic system configuration consisted of a combination of 4 basic modules<ref name=LSB0468 /><ref>Kaisler (2020), ''op. cit., p.'' 274</ref> these were:
* Processor
* System Controller
* Generalized I/O Controller (GIOC)
* Extended Memory Unit (EMU)
[[File:US3525080-GE-645-01.png|thumb|right|US3525080 Patent showing GE-645]]

The System Controller Modules (SCM) effectively acted as the heart of the system. These were passive devices which was connected to each active device (Processor, GIOC, EMU) and provided the following:<ref name=LSB0468 /><ref>Kaisler (2020), ''op. cit., p.'' 275</ref>
* Core Memory - 1 microsecond memory in size capacities of 32K, 64K or 128K of 36-bit words. 
* Centralized point for forwarding control signals from one active module to another
* System Clock and the ability to issue interrupts to the processors.

Compared to the rest of the 600 series the 645 did not use the standard IOC's (input/output controllers) for I/O. Nor did it use the [[DATANET-30]] front end processor for communications. Instead both sets of functionality was combined into one unit called a GIOC (Generalized I/O Controller) which provided dedicated channels for both Peripheral (Disc/Tape) and Terminal I/O.<ref name="LSB0468" /><ref name="Ossanna">{{cite conference |last1=Ossanna |first1=J. F. |author-link1=Joe Ossanna |last2=Mikus |first2=L. E. |last3=Dunten |first3=S. D. |book-title=Proceedings of the November 30--December 1, 1965, fall joint computer conference, Part I on XX - AFIPS '65 (Fall, part I) |title=Communications and input/Output switching in a multiplex computing system |date=30 November 1965 |pages=231–241 |doi=10.1145/1463891.1463916 |url=https://doi.org/10.1145/1463891.1463916 |publisher=Association for Computing Machinery|s2cid=15847853 }}</ref> The GIOC acted as an Active Device and was directly connected to memory via dedicated links to each System Controller that was present in a specific configuration.

The Extended Memory Unit, though termed a [[Drum memory|drum]], was in reality a large fixed-head hard disk with one head per track,<ref name="LBP">{{cite web |last1=Van Vleck |first1=Tom |title=Low Bottle Pressure |url=https://multicians.org/low-bottle-pressure.html |website=multicians.org |access-date=29 October 2023}}</ref> this was a OEM product from [[Librascope]].<ref name="LBP" /><ref>{{cite web |title=The Librazette Vol. 10 No. 9 |url=https://librascopememories.com/1960_-_1969_files/6508_RayHandOCR.pdf |archive-url=https://web.archive.org/web/20220519225513mp_/https://librascopememories.com/1960_-_1969_files/6508_RayHandOCR.pdf |archive-date=19 May 2022 |url-status=dead}}</ref> The EMU consisted of 4,096 tracks providing 4MW (megawords) of storage (equivalent to 16MB). Each track had a dedicated read/write head, these were organised into groups of 16 "track sets" which are used to read/write a sector. A sector is the default unit of data allocation in the EMU and is made up of 80 words, of which 64 words are data and the remaining 16 were used as a guard band.<ref name="LSB0468" /> The average transfer rate between the EMU and memory was 470,000 words per second, all transfers were 72-bits (two words) wide, with it taking 6.7μs to transfer 4 words.<ref name="LSB0468" /> The unit had a rotational speed of 1,725 rpm, which ensured an average latency of 17.4 milliseconds.<ref name="LSB0468" />

{| class="wikitable sortable" 
|+ GE 645 System Configurations<ref name="LSB0468" />
|-
! Component !! Small !! Typical !! Large
|-
| '''System Configuration Console'''|| 1 || 1 || 2
|-
| '''Processor'''|| 1 || 2 || 4
|-
| '''GIOC'''|| 1 || 2 || 3
|-
| '''System Controllers'''
<small>Total Capacity (Words)</small>
|| 2
128K
| 4
256K
| 8
1024K
|-
| '''Extended Memory Unit'''
<small>Total capacity (Words)</small>
|| 1
4096K
| 1
4096K
| 1
4096K
|-
| '''Fixed disc (Words)'''|| 33M || 67M || 134M
|-
| '''Magnetic Cards (Words)'''|| -- || 113M || 226M
|-
| '''Magnetic tape handlers'''|| 4 || 16 || 32
|-
| '''Printers'''|| 2 || 4 || 6
|-
| '''Card Readers'''|| 1 || 2 || 3
|-
| '''Card Punches'''|| 1 || 2 || 2
|-
| '''Perforated Tape'''|| -- || 1 || 2
|-
| '''Channels for TTY's'''|| 64 || 192 || 384
|-
| '''Channels for voice-grade communication lines''' 
'''for remote terminals such as such as''' 

'''DATANET-760 / GE-115'''
| -- || 12 || 18
|}