Hard Drives Storing Information 1 Byte at a Time

What is it? A hard disk drive (HDD) or simply hard drive stores information Much like a cassette tape, HDDs use a magnetic medium to store data

Inside a Hard Drive The two main parts of a hard drive are the platters and arms The platters are high- precision aluminum or glass disks where the magnetic recording material is added The arms have heads to read and write data

Capacity The main criteria for picking hard drives is their capacity. They are rated in terms of how many bytes they can hold This rating had moved from megabytes to gigabytes, and now terabytes (1,000,000,000,000 bytes!) of data

Reading/Writing Data Platters spin at 3,600 to 7,200 rpm The arm moves back and forth from the inside to outside of the platter at 50 times per second The allows the hard drive to write data in tracks (yellow), and sectors (blue) The sectors are grouped together into clusters

Data Organization To be useable, a hard drive needs to be formatted Low-level formatting establishes where the tracks and sectors are on the platters High-level formatting sets up the file- storage structure –FAT (File Allocation Table) –NTFS (New Technology File System)

Performance Data rate - The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common. Seek time - The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.