计算机组织与结构课件全分单元Ch061章节幻灯片.ppt

* * * * * * * * * * * * * * * * * * * * * * * William Stallings Computer Organization and Architecture6th Edition Chapter 6 External Memory 外部存储器 Types of External Memory Magnetic Disk 磁盘 RAID Removable Optical 光盘 CD-ROM CD-Recordable (CD-R) CD-R/W DVD Magnetic Tape 磁带 Page100 §6.1 Magnetic Disk Disk substrate(底层) coated with magnetizable material (iron oxide…rust) Substrate used to be aluminium(铝) Now glass Improved surface uniformity(一致,均匀) Increases reliability(可靠性) Reduction in surface defects Reduced read/write errors Lower flight heights (See later)(较低的飞行高度) Better stiffness(硬度好) Better shock/damage resistance (震动/损坏) Page164 Read and Write Mechanisms：电磁互变 Recording and retrieval via conductive coil(感应线圈) called a head 磁头 May be single read/write head or separate ones During read/write, head is stationary(固定的), platter rotates Write 电变磁 Read (traditional) 磁变电 Inductive Write MR Read 感应式写/磁阻式读的磁头 磁道宽度 磁化方向 记录介质 感应式写元件 写电流 读电流 MR敏感器 屏蔽 Page1645 Data Organization and Formatting Concentric rings or tracks 同心圆/磁道 Gaps between tracks Reduce gap to increase capacity Same number of bits per track (variable packing density) Constant angular velocity 恒角速度 Tracks divided into sectors 扇区 Minimum block size is one sector May have more than one sector per block Page165 Disk Data Layout 磁道间隙 扇区间隙 磁道 扇区 磁盘数据分布 Page166 Disk Velocity磁盘速度Disk Layout Methods Diagram 匀角速度(V=WR) 多带记录 Page167 匀线速度 Finding Sectors Must be able to identify start of track and sector Format disk 格式化磁盘 Additional information not available to user Marks tracks and sectors Gap1 Id Gap2 Data Gap3 Gap1 Id Gap2 Data Gap3 Track ＃ Sync Byte Head ＃ Sector ＃ CRC Sync By