Windows NT NTFS volumes store a last access timestamp for every file and directory. The NTFS driver automatically updates this timestamp every time a file is accessed, whether for reading or writing. That means that every time you browse through a folder, view folder contents, NT is busy updating the file timestamps which might be better used for other purposes. After browsing directories with large number of files, the NTFS log file gets filed. NT becomes sluggish or nonresponsive until the file system flushes the log to the hard disk. To disable Windows NT NTFS last access timestamp :

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Control\FileSystem
Name: NtfsDisableLastAccessUpdate
Type: REG_DWORD
Value: 1

This has no effect on "last modified" timestamp.