CS 121 Lecture Notes - Lecture 7: Program Counter, Printed Circuit Board, Instruction Register

• School: Pace University
• Department: Computer Science
• Course: CS 121
• Professor: Shan

Document Summary

Magnetic tapes: have been used as secondary storage but are considerably slower than a hard disk & usb flash drive, b/c of the way info is accessed. A hard disk is a direct access device since the read/write head can move, in general, directly to the info needed. A usb flash drive is also a direct access device, but nothing moves mechanically. Direct access & random access can be used interchangeably. Info on a tape can be accessed only after first getting past the intervening data: a tape must be rewound or fast-forwarded to get to appropriate position, so, a tape is considered a sequential access device. Random access memory (ram): describes memory where active programs. & data are stored: interchangeable w/ the term main memory, have direct (or random) access devices. 0, accordingly: typical cd-rom"s storage capacity ranges from (cid:888)(cid:887)0 to 900 mb.