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Further reading □ Overview □ About Ferranti □ Brochure □ Architecture □ Architecture □ 1-Level Storage □ Words □ Instructions □ Order Code □ Animated □ Hardware □ Fixed Store □ Supervisor □ Overview □ Scheduler □ Core Memory □ Atlas Card □ Atlas Console □ Console Details □ Chilton □ Chilton Atlas □ Downstairs □ Manchester □ Manchester Atlas □ London □ London Atlas □ London Software □ Atlas II □ Atlas 2 Brochure □ Titan Autocode □ Cambridge Atlas □ Closure □ Atlas Closure
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⟶ ACL ⟶ Technology ⟶ ATLAS
⟶ ACL ⟶ Technology ⟶ ATLAS
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Further reading ⇓

□ Overview □ About Ferranti □ Brochure
Architecture
□ Architecture □ 1-Level Storage □ Words □ Instructions □ Order Code □ Animated
Hardware
□ Fixed Store □ Supervisor □ Overview □ Scheduler □ Core Memory □ Atlas Card □ Atlas Console □ Console Details
Chilton
□ Chilton Atlas □ Downstairs
Manchester
□ Manchester Atlas
London
□ London Atlas □ London Software
Atlas II
□ Atlas 2 Brochure □ Titan Autocode □ Cambridge Atlas
Closure
□ Atlas Closure

Atlas Words

A single Atlas word can be used to represent any of the following:

  1. A 48-bit floating or fixed point number, with the 8 most-significant bits representing the exponent and the other 40 the mantissa.

    0 17 EXPONENT 8 947 MANTISSA

  2. Two 24-bit half-word numbers. These are taken usually as 21-bit signed integers in digits 0-20, with an octal fraction in digits 21-23.

    020 21-23 2444 45-47

  3. Eight 6-bit characters.

    05 0 611 1 1217 2 1823 3 2429 4 3035 5 3641 6 4247 7

  4. An instruction, specifying a function F (most-significant 10 bits), two index registers Ba and Bm (7 bits each) and an address N (least-significant 24 bits).

    09 F 1016 Ba 1723 Bm 2447 023 N

Addresses

The 23-bit main store address consists of

0 111 1220 21 Block number Word number in block Half-word address 22-23 Character address

The bits 12-20 define the address of an instruction within a 512-word page while the block address uniquely defines the address within the 1-level storage system. Blocks are moved from drum to store as required under the control of the Supervisor.

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