CMSC 104, LECT02 1 Machine Architecture An Introduction to Computer Components

CMSC 104, LECT02 2 Major Computer Components Central Processing Unit (CPU) Bus Main Memory (RAM) Secondary Storage I / O Devices Starting the computer

CMSC 104, LECT02 3 CPU Central Processing Unit The Brain Controls all other computer functions

CMSC 104, LECT02 4 The Bus Computer components are connected by a bus A bus is a group of parallel wires that carry control signals and data between components

CMSC 104, LECT02 5 Main Memory Main memory is made up of capacitors If the capacitor is charged, then its state is said to be 1 or ON. We could also say the the bit is set. If the capacitor does not have a charge, then its state is 0 or OFF. We could also say that the bit is reset or cleared.

CMSC 104, LECT02 6 Size of Capacitors Has decreased dramatically over the last 20 years. Now we can fit several million capacitors on a chip the size of a dime. As this technology becomes older, we can expect the price of memory to decrease. Is it already decreasing ? ABSOLUTELY !

CMSC 104, LECT02 7 Memory, the continuing saga Memory is divided into cells, where each cell contains 8 bits. Remember that 8 bits is called a byte. Each of these cells is numbered. The number associated with a cell is known as its address. Volatile storage

CMSC 104, LECT02 8 Reading & Writing In addition to the circuitry that holds the bits, there are other circuits that allow other components to oGet the value of the data held at a particular address - known as a READ. oOR store data at that address - known as a WRITE.

CMSC 104, LECT02 9 Memory Access All addresses in memory can be accessed in the same amount of time. We DO NOT have to start at address 0 and read everything until we get to the address we really want. We can go directly to the address we want and access the data. That is why we call Main Memory RAM - Random Access Memory

CMSC 104, LECT02 10 Secondary Storage Disks -- floppy, hard, removable Tapes (sequential access) CDs Stores files oprograms odata files (binary, text) odirectory structure Persistent storage

CMSC 104, LECT02 11 I/O I/O is handled by peripheral devices. A peripheral device is some machine that is not an integral part of the computer. Examples: omonitor okeyboard omouse odisk drive oprinter oscanner

CMSC 104, LECT02 12 Media Many I/O devices work in conjunction with media A medium holds information (programs, data, text files) Examples: floppy disk (not the drive itself) hard disk (not the drive itself) magnetic tape (not the drive itself)

CMSC 104, LECT02 13 Bits, Bytes, and Words A byte is 8 bits A word is 32 bits or 4 bytes Long word = 8 bytes = 64 bits Quad word = 16 bytes = 128 bits Programming languages use these standard number of bits when organizing data storage and access. What do you call 4 bits ?? (hint: it is a small byte)

CMSC 104, LECT02 14 Booting the Computer The term boot comes from the expression pulling yourself up by your bootstraps. It refers to the computer’s start-up procedure. When the computer is first turned on, it reads start-up instructions found in the ROM chips.

CMSC 104, LECT02 15 Booting the Computer (continued) These instructions cause the computer to do a series of tests. Each of the components is tested. The last thing that happens during boot is that the operating system is loaded from the hard disk into RAM. The computer cannot do anything until the operating system is loaded, because the operating system manages all of the basic functions of the computer.